The invention relates to an insertion electrode device for installing a sensor electrode (also referred to as sensor probe) in a container for a measuring medium. The assembly includes a probe housing (also referred to as probe holder) that can be attached to the container and contains a probe protector tube which serves to receive, hold and guide a sensor probe. The probe has a coupling for electrical connections, and the probe housing has a protective sleeve that can be connected to the probe protector tube to protect the electrical coupling from mechanical stress and moisture.
The types of sensor probes used in insertion electrode devices of this kind include oxygen probes, pH-measuring probes, conductivity probes, etc. The probes consist mostly of glass. In process control applications, the probes are installed with preference in reactors, mixing containers, or flow-through pipes, where the probes serve to determine characteristic parameters of a measuring medium contained in one of the aforementioned vessels or conduits. To perform this function, a probe is installed in a housing or holder. The probe holder serves to hold, guide and protect the probe. In particular, the probe holder establishes a connection between the probe and the container in which the probe is installed, i.e. for example a reactor, a mixing container or a flow-through pipe. A distinction is made between so-called static probe holders and retractable probe holders or housings. With the latter, the installed probe can be retracted into a rinsing chamber and cleaned during the process that the probe serves to monitor.
A so-called static probe holder does not offer the possibility of cleaning the probe during a process. It serves only to hold, guide and protect the probe. A probe housing or probe holder of this type is described in CH 673 895 A5. The housing in CH 673 895 A5 is part of a glass electrode device or insertion electrode device, for example for pH measurements or redox measurements. The housing consists of a housing top and a housing bottom, where the latter is configured as an immersion tube. The housing top can be attached to a socket of a reactor vessel, for example by means of a sleeve nut. A sensor probe, for example a glass electrode, is arranged inside the housing with the electrode shaft extending through the immersion tube and protruding into the medium inside the reactor vessel. The glass electrode is secured in the housing by means of a nut and a back-up ring.
A retractable holder or housing which is operated by compressed air is disclosed in EP 0 590 290 A1. It is equipped with a safety device which prevents the actuation of the retractable housing by letting the pressurized air escape through an opening when no sensor probe is installed, but keeps the opening closed when a probe is seated in the housing.
FIG. 1 represents, partly in a sectional view (in the left-hand part of the drawing), an example of a insertion electrode device 1 according to the state of the art. The device includes a static probe holder 3 that is suitable for installing a probe 2, in particular a glass electrode. The static probe holder 3 surrounding the probe 2 consists of a probe protector tube 4 and a protective sleeve 5. Near the end that faces towards the container in which the probe 2 is to be installed, the probe holder 3 has a process adapter 6 which is configured as a sleeve nut in the illustrated example. The process adapter 6 serves to screw the probe holder 3 to a connector socket (not shown in the drawing) of a container. Thus, a part of the probe protector tube reaches into the container (likewise not shown in the drawing). A probe 2, which is seated in the probe protector tube 4 extends likewise into the container and protrudes from the probe protector tube 4, so that a membrane 7 at the tip of the probe is immersed in the measuring fluid. A seal ring 8 prevents measuring fluid from entering between the probe 2 and the probe protector tube 4. A further seal ring 9 serves to seal the probe protector tube against the socket of the container. A third ring 18 retains the process adapter 6, so that the process adapter can move but remains captive in its position on the probe protector tube 4.
At the end of the probe 2 which during a process is located outside of the container, i.e., below the process adapter 6 in the representation of the drawing, the probe 2 has a probe header 10 with a connector terminal 11 (not shown in detail in FIG. 1) that connects to a plug 12 of an electrical cable 13. The probe header 10 has a hexagonal portion 19, so that it can be gripped and held by hand when connecting the cable plug. The plug 12 has a knurled sleeve 17 with an internal thread (not visible in FIG. 1) which screws onto an external thread (likewise invisible in the drawing) of the connector terminal 11 to secure the connection.
The probe 2 itself is screwed into the probe protector tube by means of an external thread 20 that mates with an internal thread 21 at the end of the probe protector tube that faces away from the process container. The same end of the probe protector tube 4 carries an external thread 24 which serves to attach a protective sleeve 5. For the purpose of this connection, the protective sleeve 5 is equipped with an internal thread 23 which is preferably formed in a connector part 22 which is solidly attached to the protective sleeve 5, for example by and adhesive bond. Of course, the protective sleeve could also be made of one piece. As an additional measure, a sealing compound is applied to the screw connection between the protective sleeve 5 and the probe protector tube 4, which serves in particular to prevent moisture from penetrating into the area of the electrical connection of the probe 2. When separated from the probe protector tube 4, the protective sleeve 5 can be moved along the cable 13 as well as turned about the cable 13 for making the screw connection, as the passage of the cable through the protective sleeve 5 is formed by a grommet 31 which can consist of rubber, so that it forms a good seal but is flexible at the same time.
From the foregoing description, one can establish for example the following procedure for the installation of a probe holder 3 on a container and the installation of a probe 2 in the probe holder according to the state of the art.    A. Insert the probe protector tube 4 into the connector socket and attach the process adapter 6 to the connector socket.    B. Insert the probe 2 into the probe protector tube 4 and screw the probe 2 tightly into the internal thread 21.    C. Connect the plug 12 to the socket 11 of the probe header 10 and screw the knurled sleeve 17 tightly in place    D. Screw the protective sleeve 5 onto the probe protector tube 4, applying a sealing compound to the screw threads.
However, the design of the insertion electrode device is also compatible with an installation procedure in which the aforementioned steps are performed in a different sequence. One could for example switch the steps B and C.
The disassembly is performed in reverse sequence, and it is again possible to switch the sequence of steps. It could occur, for example, that after unscrewing the protective sleeve 5 from the sleeve protector tube 4, a user may intend to loosen the screw connection of the knurled sleeve 17 which holds the plug 12 connected to the terminal 11, but if the user neglects to hold the probe 2 by its hexagonal portion 19, he could inadvertently loosen the screw connection between the probe header 10 and the probe protector tube 4, and thereby remove the entire probe 2 together with the plug connection from the probe housing 3. Removing the probe while a process is running, could have disastrous consequences. For example, the chemicals in the reactor could escape to the outside, which is particularly dangerous if the process in the reactor runs at above-ambient pressure. One cannot ignore the risk of personal injury that exists under these conditions.